Translocation


A translocation is a chromosomal aberration where a piece of DNA is excised from one chromosome and inserted into a different (non-homologous) one. Translocations may lead to the fusion of otherwise separated genes, a phenomenon which is common in cancer.

Translocations may be reciprocal, where material is exchanged between chromosomes, or Robertsonian, where there is fusion between two acrocentric chromosomes at the centromere with the loss of the small arms. Furthermore, translocations may be balanced, where the exchange is equal and there is no loss or gain of genetic material, or unbalanced, where the exchange is uneven resulting in extra or missing genes.

Reciprocal translocations are usually an exchange of material between non-homologous chromosomes. They are found in about 1 in 625 human newborns. Such translocations are usually harmless and may be found through prenatal diagnosis. However, carriers of balanced reciprocal translocations have an increased risk of creating gametes with unbalanced chromosome translocations, leading to miscarriage or children born with various abnormalities. Genetic counselling is often offered to families that may carry a translocation. Most carriers of balanced translocations don't have any symptoms and are healthy, but about 6% of them may have symptoms including autism, intellectual disability and congenital anomalies. A gene disrupted or disregulated at the breakpoint of the translocation carrier is likely to be the cause of these symptoms.